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Distant danger Scientists are concerned that debris around the distant world Pluto could damage or even destroy a multi-million dollar probe.

The concern is so great that managers have started working to determine the level of threat being faced by NASA's New Horizons spacecraft, and whether it might be necessary to change course.

Travelling at more than 54,500 kilometres per hour, New Horizons is almost seven years into its nine-and-a-half year journey across the solar system to explore Pluto and its system of moons, the first-ever exploration of a planetary body in the Kuiper Belt.

In January 2015, the spacecraft will begin its final approach culminating in a flyby of Pluto on 14 July 2015.

Scientists have become increasingly concerned that a collision with something as small as a millimetre-sized grain of rock and ice could cripple or destroy the spacecraft.

New Horizons principal investigator, Dr Alan Stern from the Southwest Research Institute in Texas, wants to steer clear of any planetary rings or debris zones that may exist around the frozen world.

"We've found more and more moons orbiting near Pluto, the count is now up to five," says Stern.

"These moons, and those not yet discovered, act as debris generators that populate the Pluto system with shards from small, colliding objects."

Potential 'black widow'

Mission managers are using sophisticated computer simulations to try and determine where the debris could be.

The data is then combined with observations of the Pluto system using both powerful ground-based telescopes and images from the Hubble Space Telescope.

At the same time, the team is plotting alternative, more distant courses through the Pluto system.

Scientists would prefer to fly closer rather than farther from Pluto.

But a bail-out trajectory would allow the mission to accomplish most of its main objectives, if the current flyby plan is found to be too hazardous.

"We're worried that Pluto and its system of moons, the object of our scientific affection, may actually be a bit of a black widow," says Stern.

"We may not know whether to fire our engines on New Horizons and bail out to safer distances until just 10 days before reaching Pluto, so this may be a bit of a cliff-hanger."